REVIEW New Zealand's Historically Rare Terrestrial Ecosystems Set in A

WILLIAMSAvailable on-line ET AL.:at: http://www.newzealandecology.org/nzje/ PHYSIOGNOMIC FRAMEWORK FOR RARE ECOSYSTEMS 119 REVIEW New Zealand’s historically rare terrestrial ecosystems set in a physical and physiognomic framework Peter A. Williams1*, Susan Wiser2, Bev Clarkson3 and Margaret C. Stanley4 1Landcare Research, Private Bag 6, Nelson 7010, New Zealand 2Landcare Research, PO Box 40, Lincoln 7640, New Zealand 3Landcare Research, Private Bag 3127, Waikato Mail Centre, Hamilton 3240, New Zealand 4Landcare Research, Private Bag 92170, Auckland Mail Centre, Auckland 1142 *Author for correspondence (Email: [email protected]) Published on-line: 3 December 2007 __________________________________________________________________________________________________________________________________ Abstract: Terrestrial ecosystems that were rare before human colonisation of New Zealand often have highly specialised and diverse flora and fauna characterised by endemic and nationally rare species. Although many of these ecosystems are under threat from anthropogenic modification and their biodiversity values are declining, they still are not adequately identified by current land classifications. We compiled a list of 72 rare ecosystems from the literature and by canvassing New Zealand ecologists and land managers. Rare ecosystems are defined as those having a total extent less than 0.5% (i.e. < 134 000 ha) of New Zealand’s total area (268 680 km2), and the resultant list includes both well-recognised and less well known ecosystems. To define the ecosystems in a robust fashion we developed a framework based on descriptors of physical environments that distinguish rare ecosystems from each other and from more common ecosystems. Using this framework the 72 rare ecosystems are defined using pertinent environmental descriptors selected from soil age, parent material, soil chemistry and particle size, landform, drainage regime, disturbance, and climate. For each ecosystem, an example locality and ___________________________________________________________________________________________________________________________________the dominant vegetation structural type are also given. Keywords: ecological classification; New Zealand; rarity; threatened terrestrial ecosystems Introduction Many of these ecosystems were historically rare, i.e. rare prior to human colonisation of New Zealand. They New Zealand’s complex topography and climate have do not include ecosystems in common environments that created a diverse array of terrestrial ecosystems. Many are now rare because of stochastic events, however; for of these are small, widely dispersed, and often lack example, distinct tree species combinations on isolated trees due to extreme environments. These distinctive mountain tops, or ecosystems largely destroyed during ecosystems may exhibit corresponding extremes of the human period, such as kahikatea (Dacrycarpus biotic diversity (i.e. have diverse flora or fauna or dacrydioides) forest on alluvium. ‘Rare’ encompasses ecosystems that are small in be particularly depauperate), may have high national 2 endemism (e.g. Carex ophiolithica and Coprosma size (e.g. 100 m to a few hundreds of hectares) but spathulata subsp. hikuruana and other endemics geographically widespread (e.g. dune deflation hollows on ultrabasic cliffs in Northland), and may support along the New Zealand coast), to those that are larger (e.g. specialised life forms (e.g. halophytes in salt pans, ten thousands of hectares) but geographically restricted tropical taxa in geothermal areas). Furthermore, these (e.g. frost flats on the volcanic plateau) (cf. Rabinowitz ecosystems often provide important refuges for native 1981). We limit the total extent of any individual type of historically rare ecosystem to less than 0.5% (i.e. < plant and animal species within highly modified 2 landscapes (e.g. braided riverbeds – Williams & 134 000 ha) of New Zealand’s total area (268 680 km ). Wiser 2004; frost flats – Smale 1990; saline patches Our geographic scope includes the main islands of New – Rogers et al. 2000; tors, cliffs and scarps – Rogers Zealand – North, South and Stewart. (More remote islands & Walker 2002). such as the Kermadec Islands, subantarctic islands, and the Chatham Islands are excluded.) New Zealand Journal of Ecology (2007) 31(2): 119-128 ©New Zealand Ecological Society 120 NEW ZEALAND JOURNAL OF ECOLOGY, VOL. 31, NO. 2, 2007 We use the definition of an ecosystem suggested (e.g. sand dunes). These classifications based on abiotic in Henderson & Henderson (1963) as an ‘ecological criteria were not designed to identify historically rare system formed by the interaction of co-acting organisms environments, however. First, the current resolution (for and their environment’. An ecosystem type is therefore LCDB2 and LENZ the minimum mapping units are 1 ha one type of ecological system that can be differentiated and 25 m, respectively) cannot detect environments such from another ecological system by one or more abiotic as ephemeral wetlands bordering karst lakes, which are or biotic factors. Groups of organisms that co-occur patches only metres across. Second, there are aspects within the ecosystem and interact through trophic or of the environment that are not represented by LENZ spatial relationships are considered to be communities (e.g. geothermal environments). Third, planar maps of (Lincoln et al. 1982). The microhabitats of individual surface projections cannot depict subterranean systems organisms, such as logs on a forest floor, are at too fine and vertical surfaces, such as cliffs. Last, tools such as a scale to be classed as ecosystems for our purposes. LENZ do not utilise biotic drivers (e.g. the effects of Collectively, historically rare ecosystems marine mammals) to identify rare environments such contain half of New Zealand’s nationally threatened as those associated with seal colonies. Consequently, plant species (PA Williams unpubl., based on data a system that is complementary to LENZ is required of de Lange et al. 2004). Similarly, 38% of the 160 to define and name physical environments of nationally threatened Lepidoptera live in ecosystems terrestrial ecosystems that were historically rare in that are themselves limited in distribution nationally New Zealand. (e.g. Dugdale 2001). This rarity at different trophic levels increases both the intrinsic interest and the Vegetation importance of rare ecosystems as foci for attention The Atkinson (1985) system for naming and delineating in biodiversity conservation initiatives (e.g. DOC & vegetation types is widely used in New Zealand MfE 2000, 2007). and is applicable to all terrestrial ecosystems. It Historical and recent losses of indigenous cover comprises two components, species composition and have been well documented by Walker et al. (2006), vegetation structure (or substrate where vegetation but data pertaining to loss of individual rare ecosystems is sparse or absent), and can be applied at a range of are lacking. Historically rare ecosystems face many scales. Vegetation has often been used as a surrogate threats, e.g. housing development (coastal sand dunes), measure for biota in natural ecosystems as vegetation weed invasions (braided riverbeds), and agricultural is immobile, easy to measure, and provides habitat for development (salt pan vegetation). Greater community most other biota (Myers et al. 1987). and agency awareness of historically rare ecosystems and their importance will hopefully lead to greater Ecosystem protection and appropriate management that will arrest their decline. Two of the better known New Zealand classification To these ends we provide an initial list of historically systems concern only forests (McKelvey 1984) and rare ecosystems and a consistent framework for wetlands (Johnson & Gerbeaux 2004). However, a delineating and mapping them. system developed to apply to the full array of ecosystem types evolved during the Protected Natural Areas Programme (PNAP) (Kelly & Park 1986; Myers et al. 1987). This classification was designed to identify Existing classifications representative examples of the full range of natural Existing classifications can be grouped broadly ecosystems within each ecological district, with the into those based on abiotic criteria, vegetation, or ultimate goal of enhancing biodiversity conservation ecosystems. (McEwen 1987). It is a hierarchical system and uses expert knowledge to subdivide each ecological district Abiotic into ecological classes (defined by bioclimatic zone, hydrologic class, and land system and vegetation Existing national environmental and land-cover structure). Ecological classes are further subdivided into classifications (e.g. Land Environments of New Zealand ecological units, which describe specifics of landforms, (LENZ; Leathwick et al. 2003) and the Land Cover and vegetation (Atkinson 1985) types. The PNAP Database (LCDB; Thompson et al. 2004) are applicable approach has provided some intuitively sound regional to common and dominant environments and vegetation. classifications (e.g. Courtney & Arand 1994), but no Nevertheless, some environments that we consider rare synthetic work has been done to enable classifications have been identified and mapped by these classifications. to be scaled up from a regional to national scale and For example, LCDB2 identifies braided riverbeds and hence to be applicable to rare ecosystems nationally. screes, and LENZ identifies ultrabasics and other areas within which rare

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